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.TH SEM.H 3HEAD "Sep 10, 2004"
.SH NAME
sem.h, sem \-  semaphore facility
.SH SYNOPSIS
.LP
.nf
#include <\fBsys/sem.h\fR>
.fi

.SH DESCRIPTION
.sp
.LP
The <\fBsys/sem.h\fR> header defines the following constants and structures.
.sp
.LP
Semaphore operation flags:
.sp
.ne 2
.na
\fB\fBSEM_UNDO\fR\fR
.ad
.RS 12n
Set up adjust on exit entry.
.RE

.sp
.LP
Command definitions for the \fBsemctl()\fR function are provided as listed
below. See \fBsemctl\fR(2).
.sp
.ne 2
.na
\fB\fBGETNCNT\fR\fR
.ad
.RS 11n
Get \fBsemncnt\fR.
.RE

.sp
.ne 2
.na
\fB\fBGETPID\fR\fR
.ad
.RS 11n
Get \fBsempid\fR.
.RE

.sp
.ne 2
.na
\fB\fBGETVAL\fR\fR
.ad
.RS 11n
Get \fBsemval\fR.
.RE

.sp
.ne 2
.na
\fB\fBGETALL\fR\fR
.ad
.RS 11n
Get all cases of \fBsemval\fR.
.RE

.sp
.ne 2
.na
\fB\fBGETZCNT\fR\fR
.ad
.RS 11n
Get \fBsemzcnt\fR.
.RE

.sp
.ne 2
.na
\fB\fBSETVAL\fR\fR
.ad
.RS 11n
Set \fBsemval\fR.
.RE

.sp
.ne 2
.na
\fB\fBSETALL\fR\fR
.ad
.RS 11n
Set all cases of \fBsemval\fR.
.RE

.sp
.LP
The \fBsemid_ds\fR structure contains the following members:
.sp
.in +2
.nf
struct ipc_perm sem_perm     /* operation permission structure */
unsigned short  sem_nsems    /* number of semaphores in set */
time_t          sem_otime    /* last \fBsemop()\fR time */
time_t          sem_ctime    /* last time changed by \fBsemctl()\fR */
.fi
.in -2

.sp
.LP
The \fBpid_t\fR, \fBtime_t\fR, \fBkey_t\fR, and \fBsize_t\fR types are defined
as described in <\fBsys/types.h\fR>. See \fBtypes.h\fR(3HEAD).
.sp
.LP
A semaphore is represented by an anonymous structure containing the following
members:
.sp
.in +2
.nf
unsigned short semval     /* semaphore value */
pid_t          sempid     /* process ID of last operation */
unsigned short semncnt    /* number of processes waiting for \fBsemval\fR
                             to become greater than current value */
unsigned short semzcnt    /* number of processes waiting for \fBsemval\fR
                             to become 0 */
.fi
.in -2

.sp
.LP
The \fBsembuf\fR structure contains the following members:
.sp
.in +2
.nf
unsigned short sem_num     /* semaphore number */
short          sem_op      /* semaphore operation */
short          sem_flg     /* operation flags */
.fi
.in -2

.sp
.LP
All of the symbols from <\fBsys/ipc.h\fR> are defined when this header is
included. See \fBipc.h\fR(3HEAD).
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
.TE

.SH SEE ALSO
.sp
.LP
.BR semctl (2),
.BR semget (2),
.BR semop (2),
.BR ipc.h (3HEAD),
.BR types.h (3HEAD),
.BR attributes (7),
.BR standards (7)
